Self-assembled glucosamine monolayers as biomimetic receptors for detecting WGA lectin and influenza virus with a quartz crystal microbalance

Abstract

N-Acetylglucosamine (GlcNAc) is a natural ligand that interacts with the binding sites of wheat germ agglutinin (WGA) lectin. For immobilization, GlcNAc was linked to p-nitrophenol, and the nitro group was reduced and then bound to cysteine via two-step synthesis. Scanning tunneling microscopy studies revealed proper immobilization of the ligand on the gold surface of a quartz crystal microbalance (QCM) via the cysteine S–H bond as well as binding between GlcNAc and WGA. QCM measurements revealed that maximum sensitivity towards WGA can only be achieved when co-immobilizing one part ligand and 5,000 parts cysteine for steric reasons, because it allows binding of a protein monolayer on the surface. Langmuir-type treatment of the binding isotherm suggests two different binding ranges for WGA and the GlcNAc monolayer, because at concentrations of WGA below 1 μm the Gibbs energy for the binding process is one third higher than that at concentrations above this value. The same systems can be transferred to first proof-of-concept measurements with different strains of influenza A virus (H5N3, H5N1, H1N3) because GlcNAc is part of the oligosaccharide ligand responsible for the first binding step. Thus, it constitutes both a suitable tool for rapid analysis and the basis for future theoretical calculations of ligand–virus interactions.